This invention relates to the field of orthogonal frequency-division multiplexing (OFDM) and, more particularly, to mode detection of OFDM signals.
In OFDM systems such as digital video broadcast (DVB) systems, each symbol has a predetermined length and is transmitted as part of a transmission block. In order to counteract multi-path distortions (reflected signals that are received after the primary signal is received), most systems incorporate a redundant portion into each transmission block. This redundant portion is generally known as a guard interval and is usually expressed as a fraction of the symbol length.
Some OFDM receivers are capable of receiving different types of OFDM signals. In order to properly demodulate a received signal, such a device must be able to identify what mode (symbol length and guard interval size) was used to generate the signal. For example, if a device is designed to receive OFDM signals with a symbol length of 2048, 4096 or 8192 samples and a guard interval that is ¼, ⅛, 1/16 or 1/32 of each symbol length, there are 12 different combinations of parameters (or modes) that the device must be able to recognize. Traditionally, OFDM receivers perform a different correlation for each mode, and the correlation having the maximum peak amplitude will be used to identify the appropriate mode. However, this approach is computationally intensive and may sometimes fail to identify the correct mode.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.